Chapter 5Data Manipulation and

Transaction Control

Oracle 10g: SQL

Oracle 10g: SQL 2

Objectives

• Use the INSERT command to add a record to an existing table

• Understand constraint violations during data manipulation

• Use a subquery to copy records from an existing table

• Use the UPDATE command to modify the existing rows of a table

• Use substitution variables with an UPDATE command

Oracle 10g: SQL 3

Objectives (continued)

• Delete records• Manage transactions with transaction

control statements COMMIT, ROLLBACK, and SAVEPOINT

• Differentiate between a shared lock and an exclusive lock

• Use the SELECT…FOR UPDATE command to create a shared lock

Oracle 10g: SQL 4

INSERT Command

• Used to add rows to existing tables

• Identify the table in the INSERT INTO clause

• Specify data in the VALUES clause

• Can only add one row at a time to a table

Oracle 10g: SQL 5

INSERT Command Syntax

• Enclose nonnumeric data in single quotes• If a column list is not provided, a value must

be assigned to each column in the table

Oracle 10g: SQL 6

INSERT Command Examples

No Column List

Column List

Oracle 10g: SQL 7

Inserting NULL Value

• Omit column name from INSERT INTO clause column list

• Substitute two single quotation marks• Use NULL keyword

NULL value input

Oracle 10g: SQL 8

Constraint Violations

• When you add or modify table data, the data is checked for compliance with any applicable constraints

Oracle 10g: SQL 9

Constraint Violations (continued)

Oracle 10g: SQL 10

Constraint Violations (continued)

Oracle 10g: SQL 11

Inserting Data from an Existing Table

• Substitute subquery for VALUES clause

Subquery

Oracle 10g: SQL 12

Modifying Existing Rows

• Modify rows using UPDATE command

• Use UPDATE command to:– Add values to an existing row (replace NULL

values)– Change existing values

Oracle 10g: SQL 13

UPDATE Command

• UPDATE clause identifies table

• SET clause identifies column(s) being changed and new value(s)

• Optional WHERE clause specifies row(s) to be changed – if omitted, all rows will be updated!

Oracle 10g: SQL 14

UPDATE Command Syntax

Oracle 10g: SQL 15

UPDATE Command Example

Oracle 10g: SQL 16

Substitution Variables

• Prompts user for value

• Identified by ampersand (&) preceding variable name

• Can be used to create interactive scripts

Oracle 10g: SQL 17

Substitution Variable Example

Oracle 10g: SQL 18

Deleting Rows

• DELETE command removes a row from a table

WHERE clause determines which row(s) are removed

Oracle 10g: SQL 19

DELETE Command – Omitting WHERE Clause

• Omitting WHERE clause removes all rows• Example below removes all rows from the acctmanager2

table

Oracle 10g: SQL 20

Transaction Control Statements

• Results of Data Manipulation Language (DML) are not permanently updated to a table until explicit or implicit COMMIT occurs

• Transaction control statements can:– Commit data through COMMIT command– Undo data changes through ROLLBACK

command

Oracle 10g: SQL 21

COMMIT Command

• Explicit COMMIT occurs by executing COMMIT;

• Implicit COMMIT occurs when DDL command is executed or user properly exits system

• Permanently updates table(s) and allows other users to view changes

Oracle 10g: SQL 22

ROLLBACK Command

• Used to “undo” changes that have not been committed

• Occurs when:– ROLLBACK; is executed– System restarts after a crash

• SAVEPOINT marks a specific spot within the transaction

• Can ROLLBACK to a SAVEPOINT to undo part of the transaction

Oracle 10g: SQL 23

Transaction Control Example

Oracle 10g: SQL 24

Transaction Control Example

Only undo DML actions after SAVEPOINT

Oracle 10g: SQL 25

Table Locks

• Prevents users from changing same data or objects

• Two types:– Shared – prevents DML operations on a portion

of table– Exclusive – locks table preventing other

exclusive or shared locks

Oracle 10g: SQL 26

LOCK TABLE Command Shared Lock

• Locks portion of table affected by DML operation

• Implicitly occurs during UPDATE or DELETE operations

• Explicitly occurs through LOCK TABLE command with SHARE MODE option

• Released when COMMIT (implicit or explicit) or ROLLBACK occurs

Oracle 10g: SQL 27

LOCK TABLE Command Exclusive Lock

• Implicitly locks table for DDL operations - CREATE or ALTER TABLE

• Explicitly locked through LOCK TABLE command with EXCLUSIVE MODE option

• Released after execution of DDL operation or after user exits system

Oracle 10g: SQL 28

LOCK TABLE Command Examples

Example-1:

The following statement locks the account managers table in shared mode:

LOCK TABLE acctmanager2 IN SHARE MODE;

Example-2:

The following statement locks the account managers table in exclusive mode:

LOCK TABLE acctmanager2 IN EXCLUSIVE MODE;

Oracle 10g: SQL 29

SELECT…FOR UPDATE Command

• Creates shared lock on retrieved portion of table

• Prevents one user from changing a row while another user is selecting rows to be changed

• Released through implicit or explicit commit

Oracle 10g: SQL 30

SELECT…FOR UPDATE Command Syntax

Oracle 10g: SQL 31

Summary

• Data manipulation language (DML) includes the INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK commands

• The INSERT INTO command is used to add new rows to an existing table

• To assign a DEFAULT option value, a column must be excluded from the column list in an INSERT

• You can change the contents of a row or group of rows with the UPDATE command

Oracle 10g: SQL 32

Summary (continued)

• DML operations are not permanently stored in a table until a commit command is issued either implicitly or explicitly

• A set of DML operations that are committed as a block is considered a transaction

• Uncommitted DML operations can be undone by issuing the ROLLBACK command

• A SAVEPOINT serves as a marker for a point in a transaction and allows only a portion of the transaction to be rolled back

Oracle 10g: SQL 33

Summary (continued)

• Use the DELETE command to remove records from a table– If the WHERE clause is omitted, all rows in the table are

deleted

• Table locks can be used to prevent users from mistakenly overwriting changes made by other users

• Table locks can be in SHARE mode or EXCLUSIVE mode

• EXCLUSIVE MODE is the most restrictive table lock and prevents any other user from obtaining any locks on the same table